The slow death of handwriting might be a boon for email-reading intelligence agencies but not for biographers, says the man entrusted by Queen Elizabeth II to write the biography of her mother.

Pulitzer Prize-nominated writer, journalist and broadcaster William Shawcross has written provocatively on an array of subjects including Cambodia, the fall of the Shah of Iran, Rupert Murdoch, the Iraq war and justice in the post 9/11 world.

Most recently Shawcross, 67, wrote the official biography of Queen Elizabeth, the Queen Mother (2009) and a compilation of some of her letters, which was released last year.

Invited by the queen to write the biography of her mother, he was given access to a full archive of her letters at Windsor Castle.

"As a journalist it's lovely getting hold of documents that no one else has got," he said in an interview with AFP on the sidelines of the Hong Kong Book Fair, where he took part in a forum on writing.

"Here was 100 years of history that people hadn't seen before."

Such paper treasure troves may themselves soon be consigned to history given the time we spend tapping on keyboards, smartphone screens and tablet computers instead of taking the time to craft missives.

Whoever gets to write the biography of Prince William -- who with his wife Catherine the Duchess of Cambridge is this week celebrating the birth of their son George -- will be in for a tough time, said Shawcross.

"Prince Charles writes long letters like his grandmother did, but Prince William sends emails and texts and that's going to be impossible for biographers."

But while the death of letter writing is going to make it "very difficult" for biographers in the future, that's not to say that the information won't be stored somewhere, he added.

"Privacy no longer exists as it did when I was young. In England we have cameras on every street corner, every text is stored forever on servers. That's a very frightening thing. I was amused to read that the Russian government is going to go back to using typewriters and paper because that's seen as less likely to be stolen".

Shawcross was referring to the Russian state service in charge of safeguarding Kremlin communications, which is looking to buy an array of old-fashioned typewriters to prevent leaks from computer hardware.

The throwback to the paper-strewn days of Soviet bureaucracy has reportedly been prompted by the publication of secret documents by anti-secrecy website WikiLeaks and the revelations leaked by fugitive former US intelligence contractor Edward Snowden.

Snowden's claims about the US National Security Agency's PRISM programme to capture and store email, phone and other communication data has raised questions of how such practices chime with democratic values while bringing into sharp focus the tension between public freedom and public safety in an increasingly wired world.

"It's a huge tension now," said Shawcross. "Everything we do is linked, we have smartphones and every text or message sent can be stored forever -- it means that there is no privacy as there was when I was growing up, and that's very sad."

Shawcross, who previously worked for The Sunday Times, examined similar ground in his 2012 book "Justice and the Enemy", which looked at the issues raised in attempting to prosecute Islamist terrorists in the post 9/11 world.

"I think Snowden was absolutely wrong to do what he has done," said Shawcross.

"His behaviour has been self-serving and damaging to the world. He could have gone up to his superiors with a perfectly proper whistleblowing process within the NSA... He should have used those other than stealing documents and releasing them in this way."

But at the very least, such behaviour might tempt a few more of us -- not to mention a few spies and royals -- into rediscovering the art of writing a letter. Future biographers would be pleased.